In a manufacturing process of a semiconductor device, various heat treatment processes such as a film forming process, a pattern etching process, an oxidation/diffusion process, a quality modification process, an annealing process and the like are repeatedly performed.
As an example of a heat treatment apparatus, Japanese Patent Laid-open Application No. 2002-327274 discloses an apparatus for forming a thin film on a surface of a semiconductor wafer serving as a target object through a gas phase chemical reaction, i.e. a CVD (Chemical Vapor Deposition) apparatus. The CVD apparatus includes a vacuum container with a heater, and the vacuum container has a stage for mounting a wafer thereon and a shower head disposed above the stage to face it. The heater is buried in the stage. In the process, the vacuum container is vacuum-evacuated to a specific vacuum level, the semiconductor wafer is heated to a specific temperature by heating the stage, and a TiCl4 gas and a H2 gas serving as a processing gas are supplied from the shower head and converted into a plasma. By using the plasma, a Ti thin film is formed on the surface of the semiconductor wafer. In this case, a hot wall process is employed to prevent TiCl4 (source material) and NH4Cl (reaction by-product) from being attached to a sidewall of the vacuum container.
In general, the vacuum container has an opening port at a top portion thereof and the opening port is closed by a lid. A sealing member is interposed between the opening port of the vacuum container and the lid to air-tightly seal a gap therebetween. An O-ring is used as the sealing member considering the ease of repair and maintenance and cost. The O-ring is generally made of elastomer with excellent heat and corrosion resistance, e.g., fluoroelastomer or perfluoroelastomer.
If an undesirable external gas, e.g., oxygen, leaks into the vacuum container during the film forming process, a vacuum level inside the vacuum container is lowered, thereby causing an adverse effect on the film forming reaction. In order to prevent this, a sealing structure to block such an undesirable gas leakage is required.
The gas enters into the vacuum container by permeating through the sealing member, and permeability of a gas in a solid is a function of a temperature of the solid. To be specific, the amount of the permeating gas decreases with a decrease of the temperature, whereas the amount of the permeating gas increases as the temperature rises. Thus, cooling the sealing member can be considered as one of possible schemes to reduce the amount of the permeating gas. Alternatively, metal with a low gas permeability can be used as the sealing member instead of elastomer.
However, in order to cool the sealing member (especially the elastomer O-ring) in case of performing the hot wall process, the walls of the vacuum container need to be heated to a specific temperature (e.g., 170° C.) while only the part where the sealing member is disposed in the walls of the vacuum container needs to be cooled. Accordingly, it is difficult to control the temperature.
Further, the metallic sealing member that secures sealing performance based on elastic deformation is plastically deformed by the repeated expansion and contraction caused by the repetition of the rise and fall of the temperature, which deteriorates the sealing performance which can be achieved by elastic deformation. Furthermore, if the material of the sealing member is different from that of the walls of the vacuum container, a sealing surface can be damaged during its expansion and contraction due to the thermal expansion coefficient difference therebetween, thereby resulting in deterioration of the sealing performance. Moreover, the metallic sealing member is more expensive than the elastomer sealing member and cannot be reused. Accordingly, the metallic sealing member is not suitable for the above-described use.